Cocaine esterase (CocE) is a product of the bacterium Rhodococcus sp. which grows in the rhizosphere of coca plants in South America. The bacterium uses cocaine as its sole source of carbon and nitrogen, synthesizing CocE to initiate metabolism of the cocaine CocE is the most efficient enzyme (7.2 X 108) for metabolizing cocaine yet identified. It can both prevent and reverse extreme cocaine toxicity in our rodent models, and it has the potential to be developed into the first useful antagonist of cocaine's toxic effects. This proposal contains studies to continue to evaluate this enzyme in mouse and rat models of cocaine toxicity, to compare its effects with other protein-based anti-cocaine enzymes, and to use a variety of in vitro techniques, including pegylation and insertion into red blood cells, to improve this or other enzymes by reducing their antigenicity, and heat liability. These procedures are designed to prolong the enzyme's duration of action with the hopeful outcome that some insight will be obtained into how to make this substance useful in the long-term treatment of cocaine abuse.